The president files for reelection slightly earlier than his predecessors. He faces a more challenging political landscape this time around.

Reporting from Washington — President Obama's launch of his reelection campaign marked a sober entrance into a 2012 contest in which he will confront a more challenging electoral landscape than in his path-breaking 2008 victory.

Obama filed reelection papers Monday, slightly earlier in the year than the last two presidents did, an indication of both an aggressive approach and the magnitude of the task ahead. His campaign aides face the time-consuming job of reorganizing and reenergizing Obama's national grass-roots operation and filling a campaign bank account that could top $1 billion.

In an email to supporters, Obama said laying the groundwork for 2012 "must start today" — even as he maintained that he was staying "focused on the job you elected me to do."

Steve Murphy, a Democratic strategist, predicted that next year's vote would be "very close," more like the tightly contested 2000 and 2004 elections than the last, which Obama won easily. "It's not as much of an electoral walk for Barack Obama," he said. "But it's still a favorable electoral map for him."

Running to replace an unpopular Republican president, Obama benefited from a financial crisis in the final weeks of the campaign and prevailed by almost 200 electoral votes over GOP nominee John McCain. But Republicans made incursions last fall in many of the areas Obama carried. Several of those states may be out of reach already, and others will be tough to hold, strategists from both parties suggest.

An analysis by the nonpartisan Cook Political Report underscored the potential for a close race. It rated seven states Obama won last time as tossups — Nevada, Colorado, Wisconsin, Iowa, Pennsylvania, Ohio and Florida — with the outcome of the election hanging in the balance.

Obama hasn't given up on states that seem likely to return to the Republican column, such as Indiana, which he plans to visit Friday, and North Carolina, site of next year's Democratic National Convention.

Like other incumbents, Obama wants to avoid being viewed as a candidate for as long as possible to limit the scent of politics in his presidential maneuverings. He did not appear in the two-minute video that accompanied his emailed announcement, and he held no public events Monday. He did make an unannounced conference call to supporters in which he described himself as "a little older and a little wiser" than in 2008.

White House Press Secretary Jay Carney said Obama was "not focused on elections" and that there would be "plenty of time well down the road for politics."

But 2012 politics is already a significant, and growing, part of Obama's routine, and over the next 19 months he will continue to straddle a line between official duties and reelection chores.

On Tuesday, for example, he is to meet with Israeli President Shimon Peres at the White House. On Wednesday, with polls showing that rising gas prices may soon eclipse jobs as the public's top economic priority, he is to discuss oil prices during his second visit in as many months to the battleground state of Pennsylvania. He will finish the day tending to his still-vibrant African American base at a New York gala organized by the Rev. Al Sharpton.

According to national opinion polls, almost half of registered voters favor a second term for Obama. That positions him on par with or better than either George W. Bush or Bill Clinton at a similar stage in their two-term presidencies, according to the Pew Research Center, which conducted the surveys.

Obama's relatively strong position reflects his political gains since Democrats took a beating in the midterm election. He also is benefiting from the absence of a clear favorite for the Republican nomination.

Still, unemployment remains high, with some economists forecasting a jobless rate of more than 8% on election day. That would be the worst jobs figure for a presidential election in more than 75 years.

"The economy is still the biggest risk," said Linda DiVall, a Republican pollster. "If unemployment stays at 9%, and you have underemployment that effectively adds another 8 to 9%, it will affect his standing with younger voters and the middle class, and then the whole hope and change argument falls a little bit flat."

Turmoil in the Middle East is also testing Obama's leadership credentials, DiVall added, and the U.S. military deployments in Afghanistan and Iraq could create problems with his liberal base and depress Democratic turnout.

Obama's decision to file papers with the Federal Election Commission allows him to begin accepting donations for his reelection. His campaign manager, Jim Messina, recently set $350,000 fundraising targets for at least 450 big Democratic money men and women. And as soon as Obama's email went out, the campaign started selling tickets to fundraising events this month at Navy Pier in Chicago, Nob Hill in San Francisco and Sony Pictures Studios in Culver City.